The broad goal of this work is to understand the molecular mechanisms that underlie the integration of signaling pathways to effect proximal- distal (PD) growth and patterning of appendages. Despite the wide diversity and evolutionary history of arthropod and vertebrate body wall outgrowths, the signaling pathways that are involved in their patterning are conserved. However, the molecular mechanisms by which these pathways act to mediate morphogenesis are unknown. Because of the complexity and interconnectivity of these pathways, the way to unambiguously elucidate their functions is to demonstrate direct, functional interaction of effector molecules with target genes. The experiments outlined in this proposal are designed to identify genetically and characterize molecularly cis-regulatory elements that control expression of the Distal-less gene in the Drosophila leg imaginal disc, and to biochemically identify the trans-acting factors to which they respond. Distal-less appears to be a key member of the genetic program that controls limb development, and identification of the components that regulate its expression will provide a crucial molecular link between positional information provided by embryonic axes and formation of the PD axis. This work will also provide the mechanistic foundation for exploring whether appendage formation operates by similar processes in different animals.